4CH1

The Periodic Table

Principles of Chemistry

Arrangement of elements

  • The periodic table lists every chemical element ever isolated — currently over 100
  • Elements are arranged in order of increasing atomic number
  • Each successive element has one more proton (and one more electron) than the one before it
  • The columns are aligned so that elements with similar chemical behaviour sit above and below each other

Groups and periods

  • Periods are the horizontal rows, numbered 1 to 7
  • Groups are the vertical columns, numbered 1 to 7, plus 0 on the far right (sometimes called Group 8 in older notations; Edexcel uses Group 0)
  • Two links between position and electron arrangement (covered in section 2):
    • number = number of occupied electron shells
    • Group number = number of electrons in the outer shell (for Groups 1 to 7)
  • For example:
    • Period 2 elements have 2 electron shells; Period 3 elements have 3 shells
    • Group 4 elements have 4 outer electrons; Group 6 elements have 6 outer electrons
The periodic table showing group numbers across the top, period rows down the side, and a colour key for metals, non-metals, liquids and metalloids
Source: Periodic Table: Basics by Save My Exams

Atomic number as a fingerprint

  • Every element has its own unique atomic number; no two elements share one
  • The atomic number does not change during a chemical reaction; only electrons move